A number of evaluation devices and methods exist within various industries for measuring properties during and after formation of certain materials. The penetration or leakage of an enclosed first material into a second enclosing material is critically important in a number of industries and may require frequent evaluation due to the compromised integrity of the second material in terms of structural flaws and wear. In particular, the wall thickness of glass and plastic containers using non-contact reflective and/or absorptive techniques by deploying sensors and emitters to direct radiation towards the container have been addressed in the prior art, as described in U.S. Pat. App. Publication No. 2013/0268237 by Wolfe et al. However, the devices used are primarily directed to evaluating the thickness of manufactured glass and plastic containers by means of using radiation capable of passing through those materials without sustaining significant losses in the levels of such radiation or accessing more than just one external surface of such materials.
On a larger scale, some industries such as the glass, steel, and plastic industries use large furnaces to melt the raw material used for processing. These furnaces may reach a length equivalent to the height of a 20-story building. Thus, they are a key asset for manufacturers in terms of costs and operational functionality. In order to minimize the internal heat loss at high operating temperatures, these furnaces are constructed using refractory material, having very high melting temperatures and good insulation properties, to create a refractory melting chamber. However, the inner walls of the refractory chamber of the furnace will degrade during operation. The effects of this degradation include inner surface erosion, stress cracks, and refractory material diffusion into the molten material.
More importantly, the leakage of molten material into the enclosing layers of refractory material may have serious consequences to the furnace operators. Currently, there is no well-established device for deterministically measuring the level of penetration of molten material into the walls of such furnaces. As a result, manufacturers experience either an unexpected leakage of molten material through the furnace wall or conservatively shut down the furnace for re-build to reduce the likelihood of any potential leakage, based on the manufacturer's experience of the expected lifetime of the furnace. The lifetime of a furnace is affected by a number of factors, including the operational age, the average temperature of operation, the heating and cooling temperature rates, the range of temperatures of operation, the number of cycles of operation, and the type and quality of the refractory material as well as the load and type of the molten material used in the furnace. Each of these factors is subject to uncertainties that make it difficult to create accurate estimates of the expected lifetime of a furnace.
Moreover, the flow of molten material, such as molten glass, at high temperatures erodes and degrades the inner surface of the refractory material and creates a high risk for molten glass leakage through the refractory wall. A major leak of molten glass through the gaps and cracks in the furnace walls may require at least 30 days of production disruption before the furnace can be restored to operating mode because it needs to be cooled down, repaired, and fired up again. Furthermore, a leak of molten glass may cause significant damage to the equipment around the furnace and, most importantly, put at risk the health and life of workers. For these reasons, in most cases furnace overhauls are conducted at a substantially earlier time than needed. This leads to significant costs for manufacturers in terms of their initial investment and the reduced production capacity over the operational life of the furnace.
Another important issue is that the material used to build the refractory chamber of the furnace may have internal flaws not visible by surface inspection. This could translate into a shorter life of the furnace and pose serious risks during furnace operation. Accordingly, on the one hand the refractory material manufacturer would like to have a means to evaluate the material during manufacture to be able to qualify the material for furnace construction following quality standards to deliver material with no flaws. On the other hand, the customer purchasing the refractory material would like to have a means for performing internal inspections of such material before constructing a furnace.
Previous efforts have been made to use microwave signals to evaluate the status of materials such as furnace walls, as described in U.S. Pat. No. 6,198,293 to Woskov et al. and U.S. Pat. App. Pub. No. 2013/0144554 by Walton et al. However, these efforts have faced certain challenges and limitations. In particular, attempts made to use devices to evaluate the status of a furnace wall on hot furnaces have been generally unsuccessful because of the large signal losses involved in evaluating the inner surface of refractory materials, especially at relatively high frequency bands. Likewise, at relatively low frequency bands signals still experience losses and are limited in terms of the bandwidth and resolution required by existing systems. Critically, in placing system components close to the surface of the refractory material to be evaluated, spurious signal reflections make it extremely difficult to isolate the reflected signal of interest, thus further complicating the evaluation of the presence of molten material within the layers of refractory material of such furnaces. A major challenge is that furnace walls become more electrically conductive as temperature increases. Therefore, signals going through a hot furnace wall experience significant losses making the detection of these signals very challenging.
Furthermore, Ruege et al., as described in copending and co-owned U.S. patent application Ser. No. 14/226,102 titled “Material Erosion Monitoring System and Method” (the specification of which is incorporated herein by reference in its entirety), have disclosed an approach for evaluating the status of a material, based on the detection of electromagnetic waves reflected from remote discontinuities of the material. However, while this approach is effective in determining the thickness and erosion profile of different materials, including the refractory layers surrounding a furnace, to identify a flaw in the furnace walls, a major limitation may result where there is a need to determine the presence and extent of penetration of molten material within the refractory layers of the furnace. Accordingly, this approach is not able to identify or warn a user about certain leaks of molten material unless a reduction in thickness or a noticeable profile change of the refractory walls occurs. As a result, molten material may inadvertently flow throughout the furnace walls and create severe damage to the furnace without the possibility of preventing such type of situations.
Thus, there remains a need in the art for devices and methods capable of remotely evaluating the status of such refractory materials, and particularly the presence of a molten material that has leaked into one or more layers of the enclosing refractory materials, through measurements of propagating electromagnetic waves, that avoid the problems of prior art devices and methods.